Seems like $300 to $400 bucks is a typical price.
I'd think twice though. I don't really believe it's good for cars to idle much; I'd rather get in and go (gently) out of my neighborhood until everything warms up. Idling won't really help warm up the axle parts and transmission much. Cop cars and taxis seem to do ok idling though.
When I lived in Anchorage, and my cars lived outside, I used a block heater for an hour first thing in the morning. That got the engine oil warmed up a bit and helped with starts, and helped the cabin warm up faster.
And I had a $20 portable heater that I would plug in the night before when I would plug in the block heater. It would clear off the glass and warm up the car pretty fast.
Both the block heater and portable heater plugged into a switched outside outlet, so it was easy to flip the switch on my way to make coffee.
The other issue with adding an aftermarket remote starter is that problems with the alarm system or key fobs always seem to show up in 4 or 5 years. If you decide to get one, check out the reputation of the shop doing the work carefully. And keep a copy of the installation instructions.